One example of the display device is a liquid crystal display device including a TFT substrate in which pixel electrodes, thin film transistors (TFTs) and the like, are arranged in a matrix form. Then, a counter substrate is disposed opposite to the TFT substrate, in which color filters, and the like, are formed at locations corresponding to the pixel electrodes of the TFT substrate. Further, a liquid crystal layer is interposed between the TFT substrate and the counter substrate. In such a liquid crystal display device, the transmittance of light is controlled by liquid crystal molecules for each pixel to form an image.
The liquid crystal display device can be made thin and light weight, and is used in a wide range of applications. The liquid crystal does not emit light by itself, so that a backlight is provided on the back of the liquid crystal display panel. In small liquid crystal display devices, LED is used as a light source. Further, in the small liquid crystal display device, the so-called side light type backlight in which LEDs are located on a side of the light guide plate is used to reduce the thickness of the entire device.
Although the LED is a point light source, it is necessary that the light emitted from the light guide plate is an area light source. However, the light intensity greatly varies around the light guide plate in which the LEDs are located, so that it is not appropriate to use such a light guide plate as the area light source. Thus, the region that can be used as the area light source is limited. In order to increase the area that can be used as the area light source, Japanese Application Laid-Open No. 2002-169034 and Japanese Application Laid-Open No. 2005-63913 describe a configuration in which a trapezoidal projection is formed on a side of the light guide plate, and the LED as the light source is mounted on the upper bottom portion of the trapezoidal projection to obtain a uniform light emitted from the light guide plate. The backlight described in Japanese Application Laid-Open Nos. 2002-169034 and 2005-63913 uses the white LED as the light source. For this reason, the problem of color variation does not occur.
Japanese Application Laid-Open No. 2007-200876 describes a configuration in which a large number of LED sets of red-emitting LED (hereinafter referred to as red LED), green-emitting LED (hereinafter referred to as green LED), and blue-emitting LED (hereinafter referred to as blue LED) are used in the so-called direct-type backlight, in order to obtain an area light source of white color. Each LED set is mounted in a light guide part having a convex portion with a T-shaped cross section, in which a concave portion is formed on the opposite side of the convex portion. In the LED set, three color LEDs are arranged in a delta pattern in the convex portion of the light guide part. In this way, the three colors are mixed together in the light guide part.